Heart valve replacement is necessary where the native heart valve is damaged, mal- or nonfunctioning. In the heart, cardiac valves maintain the unidirectional flow of blood by opening and closing depending on the difference in pressure on each side. As such, a heart valve can be affected by a range of diseases and can, therefore, require cardiac valve replacement. The valve can either become leaky, i.e. regurgitant or insufficient, in which case the aortic valve is incompetent and blood flows passively back to the heart in the wrong direction. Further, the valve can become partially shut, i.e. stenotic, in which case the valve fails to open fully, thereby obstructing blood flow out from the heart. The two conditions frequently co-exist.
Heart valve replacement traditionally requires median sternotomy and thus open heart surgery, which is a major impact on the patient to be treated: The sternum is sawed in half and after opening of the pericardium, the patient is placed on a cardiopulmonary bypass machine. Once the patient is on bypass, the patient's diseased aortic valve is removed and a mechanical or tissue valve is put in its place. Besides the physical stress associated with this operation, there is a risk of death or serious complications from open heart surgery, in particular depending on the health and age of the patient.
However, systems have been developed which allow percutaneous introduction and deployment of prosthetic heart valves, by means of which open heart surgeries can be avoided. The deployment of such heart valve prostheses can either be achieved retrograde, i.e. against normal blood flow, or antegrade, with blood flow.
For percutaneous valve replacements, various types and configurations of prosthetic heart valves are presently used, wherein the actual shape and configuration of any particular prosthetic heart valve is dependent, on the one hand, upon the valve being replaced. Generally, the prosthetic heart valve designs attempt to replicate the function of the valve being replaced and thus will regularly include valve leaflet-like structures used with either bioprosthesis, which are usually made from animal tissues, either animal heart valve tissue or animal pericardial tissue, and which are treated to prevent rejection and to prevent calcification, or mechanical heart valve prostheses, which are generally composed entirely of synthetic or non-biological materials. As such, the replacement valves may include a valved segment that is mounted in some manner within an (self-)expandable stent structure. There are two types of stents on which the valves structures are ordinarily mounted: self-expanding stents and balloon-expandable stents. To place such valves into a delivery apparatus and ultimately into a patient, the valve must first be collapsed or crimped to reduce its circumferential size.
When a collapsed prosthetic valve has reached the desired implant site in the patient, i.e. at or near the annulus of the patient's heart valve that is to be replaced by the prosthetic valve, the prosthetic valve is deployed or released from the delivery apparatus and expanded to full operating size. With balloon-expandable valves, generally the entire valve is released and subsequently expanded by an expandable balloon positioned within the valve stent. With self-expanding valves, the deployment systems regularly comprise a retractable sheath, upon withdrawing of which the stent automatically begins to expand.
For a fully functioning prosthetic heart valve it is crucial that all of its components fulfill their respective task: The valve, on the one hand, needs to be adequately attached to the stent support, since otherwise the valve is prone to failure, and valve failure, in the circulatory system, has significant consequences for the patient. On the other hand, the stent support needs to fully expand and, thus, guarantee the secure fixation within the heart vessels.
Also, a proper fixation of the prosthetic heart valve replacing the native diseased heart valve very often is complicated due to, e.g., calcification of the native valve. The calcified valve-tissue renders irregular the annular ring, making it difficult to securely fixate the prosthetic replacement valve in the annular ring.
In view of the above, there is a constant need for improving the deployment and fixation of prosthetic heart valves in the heart to be treated, while simultaneously guaranteeing the smooth and easy release of the prosthetic heart valve in the heart vessel from the deployment system.
Thus, it is an object of the present invention to provide for a prosthetic heart valve that fulfills the requirements above and overcomes the drawbacks of the presently available heart valve prostheses.